Low pressure deethanization process and system

ABSTRACT

A system and process for separating ethane and propane from a feed stream comprising dehydrated liquefied petroleum gas is disclosed. A distillation column operates at a lower pressure and temperature than conventional distillation columns. High purity liquid propane exits the bottom of the distillation column and is flashed through a cooling control valve becoming a two-phase stream with the vapor entering a heat pump compressor. The high or increased temperature compressed propane stream exiting the heat pump compressor is directed into the distillation column to drive the separation of the ethane and propane, allowing the elimination of a reboiler from the system and process.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Application No. 61/865,138, filed Aug. 13, 2013, entitled “Low Pressure Deethanization Process and System,” which is incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

In fractionating natural gas liquids, the use of distillation columns is well known in the art. In conventional distillation processes, natural gas liquids enter the distillation column and the lighter, more volatile components move up the column while the heavier, less volatile components drop toward the bottom of the column. The vapors exiting the top of the distillation column run through a condenser. Condensed liquid is routed back to the distillation column (reflux). Overhead product is removed from the system as either a vapor or liquid as needed. The liquids exiting the bottom of the distillation column run through a heater or reboiler and any resultant vapors are routed back to the distillation column. Any remaining liquid is removed from the system as bottoms product.

SUMMARY

In one embodiment, a system having a low operating pressure for separating ethane and propane from a feed stream includes a distillation column having an upper end and a lower end that is configured to receive the feed stream and release ethane from the upper end and propane from the lower end. In addition, the system includes a feed stream control device configured to control the feed stream entering the distillation column, a heat pump exchanger configured to condense the ethane and vaporize the propane released from the distillation column, an overhead product control device configured to control the ethane exiting the system, and a reflux control device configured to distribute ethane back to the distillation column from the heat pump exchanger. The system further includes a bottoms product control device configured to control the propane exiting the system, a cooling control device configured to control an amount of propane entering the heat pump exchanger, a compressor assembly configured to compress propane vapor exiting the heat pump exchanger, and a control system configured to actuate the control devices. Moreover, the compressed propane vapor exiting the compressor assembly supplies heat to the distillation column. In some embodiments, a heat rejection device is configured to remove heat from the compressed propane vapor.

In one embodiment, a process for separating ethane and propane from a feed stream at low pressure includes introducing a feed stream to a distillation column to obtain ethane vapor and liquid propane, condensing the ethane vapor to obtain liquid ethane, removing a portion of the liquid ethane through an overhead product control device, and refluxing a portion of the liquid ethane back to the distillation column. In addition, the process includes removing a portion of the liquid propane through a bottoms product control device, flashing a portion of the liquid propane through a cooling control device to introduce vapor to the liquid propane, vaporizing the liquid propane to obtain a propane vapor, compressing the propane vapor to obtain a propane vapor having a higher temperature and pressure, and supplying heat to the distillation column using the higher temperature and pressure propane vapor. In some embodiments, the process may further include removing heat from the higher temperature and pressure propane vapor through a heat rejection system or bypassing the heat rejection system before entering the distillation column.

Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical advantages of the disclosure such that the detailed description of the disclosure that follows may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the disclosure, reference will now be made to the accompanying drawings in which:

FIG. 1 is a simplified process flow diagram of a first embodiment of a system and process for separating ethane and propane from a feed stream in accordance with the principles described herein;

FIG. 2 is a simplified process flow diagram of a second embodiment having a reflux accumulator and vapor overhead product;

FIG. 3 is a simplified process flow diagram of a third embodiment having a reflux accumulator and liquid overhead product;

FIG. 4 is a simplified process flow diagram of a fourth embodiment having a product interchanger;

FIG. 5 is a simplified process flow diagram of a fifth embodiment having an economizer;

FIG. 6 is a simplified process flow diagram of a sixth embodiment having two economizers;

FIG. 7 is a simplified process flow diagram of a seventh embodiment having a feed interchanger;

FIG. 8 is a simplified process flow diagram of an eighth embodiment having a compressor suction scrubber; and

FIG. 9 is a simplified process flow diagram of a ninth embodiment having a reflux accumulator, a product interchanger, two economizers, a feed interchanger, and a compressor suction scrubber.

DETAILED DESCRIPTION

The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosures, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function. Moreover, the drawing figures are not necessarily to scale. Certain features of the disclosure may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. Further, some drawing figures may depict vessels in either a horizontal or vertical orientation; unless otherwise noted, such orientations are for illustrative purposes only and is not a required aspect of this disclosure.

In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . . ” Also, the terms “couple”, “attach”, “connect” or the like are intended to mean either an indirect or direct mechanical or fluid connection, or an indirect, direct, optical or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct mechanical or electrical connection, through an indirect mechanical or electrical connection via other devices and connections, through an optical electrical connection, or through a wireless electrical connection.

In various embodiments to be described in detail below, a system and process for separating ethane and propane includes the use of compressed propane having a high or an increased temperature in accordance with the principles of the present disclosure. In certain embodiments, the high or increased temperature compressed propane stream directed into the distillation column allows the elimination of a reboiler from the system and process for separating ethane and propane.

Referring now to FIG. 1, in a first embodiment, a process and system 10 for deethanizing a feed stream comprises a distillation column 210, a heat pump exchanger 220, a heat pump compressor 270, a system heat rejection device 300, a plurality of control devices or control valves 200, 230, 240, 250, 260, 280, 290, 340, 360, 380, 400 in communication with a control system 500, and a plurality of fluid streams 100-134 which are described in more detail below. Each control valve includes a device to open and close the valve. The heat pump exchanger 220, compressor 270, system heat rejection device 300, and plurality of control valves are standard in the art and various commercially available units of each component may be used. More specifically, any heat pump exchanger 220 known in the art including, but not limited to, shell and tube, brazed aluminum, core-in-kettle, printed circuit, and plate and frame may be used. Any heat pump compressor 270 known in the art including, but not limited to, centrifugal, reciprocal, and screw may be used. Further, the heat rejection device 300 may be any type of heat exchange equipment known in the art that transfers heat to a lower temperature heat sink, the heat sink including, but not limited to, air, water, refrigerant, and various other coolants.

The distillation column 210 differs from distillation columns standard in the art. In the present embodiment, distillation column 210 operates at a lower pressure than conventional distillation columns. Distillation column 210 operates at a pressure preferably between 160 and 260 psig, and more preferably around 240 psig, compared to a conventional distillation column that operates above 300 psig. Further, distillation column 210 is shorter, or has a lesser longitudinal or axial dimension, than conventional distillation columns. A conventional distillation column includes a longitudinal or axial dimension which must accommodate more than 40 trays. The distillation column 210 of the present embodiment preferably has 25-40 trays, and more preferably has 30 trays. The top of distillation column 210 also operates at a lower temperature than conventional distillation columns, which typically operate at 30-50° F. Distillation column 210 of the present embodiment preferably operates at a temperature between −20° F. and 15° F., and more preferably at approximately 10° F.

The control system 500 comprises a plurality of sensors 510, 520, 530, 540, 550, 560 disposed in the various components (e.g., sensor 510 is located in the distillation column 210) and in the flowpaths between the components (e.g., sensor 520 is located in stream 110 that flows into the top of the distillation column 210; sensor 530 is located in stream 118, 119 at the inlet of the compressor 270; sensor 540 is located at the outlet of the compressor 270; sensor 550 is located in stream 114; sensor 560 is located in stream 108). The quantity and locations of the sensors 510-560 are intended as examplary only and a greater or lesser number of sensors may be employed in either the locations indicated in FIG. 1 or in various other locations across system 10. The sensors 510-560 include types known in the art and that are suitable according to the uses described below.

The control system 500 is in communication with all the actuators and sensors 510-560 and adjusts all control valves to open and close as needed based on the desired measurement parameters at each component (e.g., the distillation column 210). The control system 500 may control the valves of system 10 using any measurement parameters known in the art including, but not limited to, temperature, pressure, composition, level, or flow rate. In the following description of the preferred embodiments, the various control valves are described as controlling certain aspects of a stream; in each instance, the control system 500 is controlling and actuating the valve, but for simplicity, this step will not be described. The control system 500 will be discussed in more detail below.

Referring still to FIG. 1, the deethanization system 10 begins with a feed supply stream 100 entering a distillation column 210. A feed stream control valve 200 controls the amount of feed stream 100 entering the distillation column 210. Stream 100 comprises dehydrated liquefied petroleum gas, and may be HD-5 grade propane. Stream 100 may be dehydrated using any dehydrating agent known in the art to reduce the moisture level to less than 1.0 ppmw. In general, any dehydration agent known in the art including, but not limited to, a molecular sieve or glycol may be used.

Ethane vapor exits the top of the distillation column 210 in stream 104 and flows to heat pump exchanger 220. The heat pump exchanger 220 condenses the ethane vapor producing a liquid ethane stream 106 with a lower temperature and pressure than the ethane vapor stream 104. Stream 106 then splits with a portion exiting the system and a portion being returned to the distillation column 210. The portions of stream 106 that exit or return to the column are controlled by an overhead product control valve 230 and a reflux control valve 240, respectively. The overhead product control valve 230 controls the amount of stream 106 exiting the system as overhead product in stream 108. The reflux control valve 240 controls the amount of liquid ethane stream 106 that flows back into the distillation column 210 in reflux stream 110. Reflux stream 110 enters the top of the distillation column 210 and drives the propane down the distillation column 210.

Still referring to FIG. 1, high purity liquid propane exits the bottom of the distillation column 210 in bottoms stream 112 and splits with a portion exiting the system and a portion flowing to the heat pump exchanger 220. The portions of stream 112 that either exit or flow to the exchanger 220 are controlled by a bottoms product control valve 250 and a cooling control valve 260, respectively. The bottoms product control valve 250 controls the amount of liquid propane stream exiting the system as bottoms liquid product in stream 114. The cooling control valve 260 controls the amount of liquid propane stream 112 that flows to the heat pump exchanger 220. Stream 112 is flashed through the cooling control valve 260, entering as a single phase liquid and exiting as a two-phase liquid and vapor in stream 116. The two-phase stream 116 then enters the heat pump exchanger 220. In the heat pump exchanger 220, the propane vapors are boiled off and exit the exchanger 220 in stream 118.

Propane vapor stream 118 then enters heat pump compressor 270, which compresses the vapor stream and increases the temperature. The hot, compressed propane vapor exits the compressor 270 in stream 120. Compressor discharge stream 120 then flows into the distillation column 210. However, before the stream 120 reaches the distillation column 210, the control system 500, using heat control valve 280 and heat control bypass valve 290, may divert a portion, all, or none of the stream 120 through a system heat rejection device 300, which is configured to remove heat from the stream 120. The heat from the compressed propane vapor stream 120 is used to drive the separation of the ethane and propane in the distillation column 210. Control system 500 monitors measurement readings from sensor 510 located in distillation column 210 and sensor 540 located in the compressor discharge stream 120 after the compressor 270 to determine what portion, if any, of stream 120 will pass through the system heat rejection device 300. Various parameters may be used to set operating limits for the deethanization system 10 including, but not limited to, pressure, flowrate, composition, or temperature.

For example, if pressure is used to control the system 10, the pressure inside the distribution column 210 may be monitored via sensor 510 and when the pressure in the column 210 drops below a certain threshold, pressure control valve 290 is opened to allow stream 122 to enter the column 210 to raise the pressure. Conversely, if the pressure exceeds a certain threshold, the pressure control valve 290 is closed to allow the compressed vapor stream 120 to pass through the system heat rejection device 300 to condense more vapor from the stream 120 and reduce the pressure in the distillation column 210. Concurrently, a sensor 550 monitors the composition of stream 114. If the stream 114 contains too much ethane, the heat control valve 280 is closed to remove less heat and drive the ethane overhead. Conversely, if the propane in stream 114 is too pure, the heat control valve 280 is opened allowing more flow through the system heat rejection device 300. Depending on the pressure in the distillation column 210 and the composition of stream 114, the control system 500 may open or close valves 280, 290 partially or completely in any combination necessary to achieve the desired product composition of stream 114.

While the bottom of the distillation column 210 may be controlled as described above, the top of the distillation column 210 may be controlled as follows. Sensor 530 monitors the suction pressure of the compressor 270 on stream 118. This pressure is controlled by the compressor 270 and determines the temperature of stream 116 flowing into the heat pump exchanger 220. The flow rate of stream 116 is monitored and controlled using flow control valve 260. Stream 116 is used to condense the vapor in stream 104 creating both the reflux stream 110 and the ethane product stream 108. The composition of stream 108 may be monitored by sensor 560 for propane content. If the propane content is too high, the control system 500 will increase the flowrate of the reflux stream 110 using the flow control valve 240. Conversely, if the ethane purity is too high, the control system 500 will decrease the flowrate of the flux stream 110 using the flow control valve 240.

As previously described, system 10 does not employ a reboiler to supply heat to the distillation column 210. Instead, the heat supplied to the distillation column 210 to drive the separation of ethane and propane comes from the hot, compressed propane vapor stream 120 exiting the compressor 270, which flows into the distillation column 210. Additionally, system 10 does not employ an external refrigeration unit to cool the distillation column 210. Instead, the cooling comes from the purified propane product. Further, various devices may be used to increase the efficiency or provide additional benefit to deethanization system 10. Examples of such devices are disclosed herein.

Referring now to FIG. 2, a second embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. Similar to the first embodiment, a feed supply stream 100 enters a distillation column 210 and ethane vapor exits the top of distillation column 210 and flows to heat pump exchanger 220. However, the deethanization system 10 in this embodiment also includes a reflux accumulator device 310 and a reflux pump 320 to create an ethane vapor overhead product as opposed to an all liquid product. Both the reflux accumulator device 310 and the reflux pump 320 are standard in the art and any commercially available units of each may be used. The liquid ethane stream 106 exiting the heat pump exchanger 220 enters the reflux accumulator 310. The reflux accumulator 310 collects the liquid ethane stream 106 and removes any remaining ethane vapor via stream 107. Stream 107 is introduced to overhead product control valve 230, which as previously described controls the amount of overhead product exiting the system in stream 108. In the present embodiment, the overhead product in stream 108 exiting the system is ethane vapor. The collected liquid ethane stream 106 exits the reflux accumulator 310 as stream 109. Stream 109 then enters reflux pump 320, which introduces stream 109 to reflux control valve 240. The reflux control valve 240 controls the amount of liquid ethane stream 109 that flows back into the distillation column 210 in reflux stream 110. Reflux stream 110 enters the top of the distillation column 210 and drives the propane down the distillation column 210. The remainder of the stream flows 112, 114, 116, 118, 120, 122, 124 and components (i.e., heat pump exchanger 220, heat pump compressor 270, heat rejection device 300, and control valves 250, 260, 280, 290) of system 10 of the present embodiment are substantially the same as that of the first embodiment.

Referring now to FIG. 3, a third embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. Similar to the first two embodiments, a feed supply stream 100 enters a distillation column 210 and ethane vapor exits the top of distillation column 210 and flows to heat pump exchanger 220. The deethanization system 10 in this embodiment includes a reflux accumulator device 310 and a reflux pump 320, both standard in the art and commercially available, with a liquid ethane overhead product. The liquid ethane stream 106 exiting the heat pump exchanger 220 enters a reflux accumulator 310. The reflux accumulator 310 collects the liquid ethane stream 106, which exits the reflux accumulator 310 as stream 109. Stream 109 enters reflux pump 320, and then splits with a portion exiting the system and a portion being returned to the distillation column 210. The portions of stream 109 that exit or return to the column are controlled by an overhead product control valve 230 and a reflux control valve 240, respectively. The overhead product control valve 230 controls the amount of stream 109 exiting the system as overhead product in stream 108. In the present embodiment, the overhead product in stream 108 exiting the system is liquid ethane. The reflux control valve 240 controls the amount of liquid ethane stream 109 that flows back into the distillation column 210 in reflux stream 110. Reflux stream 110 enters the top of the distillation column 210 and drives the propane down the distillation column 210. The remainder of the system 10 of the present embodiment is substantially the same as that of the first two embodiments.

Referring now to FIG. 4, a fourth embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. The present embodiment comprises all the same process flows and components as the first embodiment with the addition of a product interchanger 330 standard in the art. The product interchanger 330 allows the product temperatures to be adjusted to suit the needs of downstream users. After overhead product stream 108 exits overhead product control valve 230 and bottoms product stream 114 exits the bottoms product control valve 250, both streams 108, 114 enter a product interchanger 330, which exchanges the cold overhead product with the warm bottoms product. Overhead product stream 108 exits the product interchanger as stream 125 and bottoms product stream 114 exits the product interchanger 330 as stream 126.

Referring now to FIG. 5, a fifth embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. The deethanization system 10 in this embodiment also includes an economizer 350 standard in the art and commercially available. Similar to the first embodiment, a feed supply stream 100 enters a distillation column 210 and ethane vapor exits the top of distillation column 210 and flows to heat pump exchanger 220 where the vapor is condensed and then fed back into the distillation column 210. High purity liquid propane then exits the bottom of the distillation column 210 in bottoms stream 112 and splits with a portion exiting the system and a portion flowing to an economizer 350. The portions of stream 112 that either exit or flow to the economizer 350 are controlled by a bottoms product control valve 250 and an economizer level control valve 340, respectively. Similar to the first embodiment, the bottoms product control valve 250 controls the amount of liquid propane stream exiting the system as bottoms liquid product in stream 114. The economizer control valve 340 controls the amount of liquid propane stream 112 that flows to the economizer 350. Stream 112 is flashed through the economizer control valve 340, entering as a single phase liquid and exiting as a two-phase liquid and vapor in stream 113. The two-phase stream 113 enters the economizer 350, which separates the liquid and vapor. The vapor exits the economizer 350 in stream 117 and, like the vapor stream 118 exiting the heat pump exchanger 220, is sent to the compressor 270, which compresses the vapor streams 117, 118. The economizer control valve 340 and economizer 350 allow the pressure of stream 117 to be maintained at a higher level. The liquid propane exits the economizer 350 in stream 115 and is introduced to the cooling control valve 260. Similar to the first embodiment, the cooling control valve 260 controls the amount of liquid propane stream 115 that flows to the heat pump exchanger 220. The remainder of the system 10 of the present embodiment is substantially the same as that of the first embodiment.

Referring now to FIG. 6, a sixth embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. The present embodiment is similar to the fifth embodiment with the economizer 350 of the fifth embodiment replaced with a high pressure (HP) economizer 370 and a low pressure (LP) economizer 390 both standard in the art and commercially available. High purity liquid propane exits the bottom of the distillation column 210 in bottoms stream 112 and is introduced to a HP economizer control valve 360, which controls the amount of liquid propane stream 112 that flows to the HP economizer 370. Stream 112 is flashed through the HP economizer control valve 360, entering as a single phase liquid and exiting as two-phase liquid and vapor in stream 127. The two-phase stream 127 enters the HP economizer 370, which separates the liquid and vapor. The vapor exits the HP economizer 370 in stream 129 and is sent to the compressor 270. The liquid propane exits the HP economizer 370 in stream 128 and splits with a portion exiting the system and a portion flowing to a LP economizer 390.

The portions of stream 128 that either exit or flow to the LP economizer 390 are controlled by a bottoms product control valve 250 and a LP economizer control valve 380, respectively. Similar to the first embodiment, the bottoms product control valve 250 controls the amount of liquid propane stream exiting the system as bottoms liquid product in stream 114. The LP economizer control valve 380 controls the amount of liquid propane stream 128 that flows to the LP economizer 390. Stream 128 is flashed through the LP economizer control valve 380, entering as a single phase liquid and exiting as a two-phase liquid and vapor in stream 130. The two-phase stream 130 enters the LP economizer 390, which separates the liquid and vapor. The vapor exits the LP economizer 390 in stream 132 and, like the vapor stream 118 exiting the heat pump exchanger 220 and the vapor stream 129 exiting the HP economizer 370, is sent to the compressor 270, which compresses the vapor streams 118, 129, 132. The liquid propane exits the LP economizer 390 in stream 131 and is introduced to the cooling control valve 260. Similar to the first embodiment, the cooling control valve 260 controls the amount of liquid propane stream 131 that flows to the heat pump exchanger 220. The remainder of the system 10 of the present embodiment is substantially the same as that of the first embodiment.

Though shown in the present embodiment with two economizers 370, 390, in other embodiments additional economizers may be used.

Referring now to FIG. 7, a seventh embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. The present embodiment comprises many of the same process flows and components as the first embodiment with the addition of a feed interchanger 410 standard in the art. Feed interchanger 410 allows system 10 to accommodate extreme feed stream 100 temperatures and swings in temperatures without negative impact on the distillation column 210. Feed supply stream 100 enters a feed interchanger 410 prior to entering the distillation column 210. The feed interchanger 410 regulates the temperature of the feed stream entering the distillation column. An incoming feed stream 100 that is very hot or very cold can flood the distillation column 210 either in the top (if very hot) or bottom (if very cold) of the column 210. The feed interchanger 410 takes some or all of the bottoms stream 112 exiting the bottom of the distillation column 210 (the other portion of bottoms stream 112 exits the system in bottoms liquid product stream 114 via bottoms product control valve 250). A feed interchanger control valve 400 controls the amount of bottoms stream 112 that flows to the feed interchanger 410. The bottoms stream 112 then exchanges heat with the feed supply stream 100 in the feed interchanger 410 to either reduce or increase the temperature of the feed stream 100 depending on whether the feed stream temperature is higher or lower than the temperature of the bottoms stream 112. For example, if the feed stream 100 has a very high temperature, bottoms stream 112 reduces the temperature of the feed stream 100, resulting in a reduced-temperature feed stream exiting the feed interchanger 410 as regulated stream 102 and a higher vapor fraction bottoms stream 112 exiting the feed interchanger 410 as interchanged stream 133. Conversely, if the feed stream 100 has a very low temperature, bottoms stream 112 increases the temperature of the feed stream 100, resulting in an increased-temperature feed stream exiting the feed interchanger 410 as regulated stream 102 and an reduced-temperature bottoms stream 112 exiting the feed interchanger 410 as interchanged stream 133.

The regulated stream 102 exits the feed interchanger 410 and enters the distillation column 210. Similar to the other embodiments, a feed stream control valve 200 controls the amount of regulated stream 102 entering the distillation column 210. Ethane vapor then exits the top of distillation column 210 and flows to heat pump exchanger 220 where the vapor is condensed and then fed back into the distillation column 210.

Referring still to FIG. 7, the interchanged stream 133 exits the feed interchanger 410 and flows to the heat pump exchanger 220. The remainder of the system 10 of the present embodiment is substantially the same as that of the first embodiment.

Referring now to FIG. 8, an eighth embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. The present embodiment comprises all the same process flows and components as the first embodiment with the addition of a compressor suction scrubber 420 standard in the art and commercially available. Compressor suction scrubber 420 protects the compressor 270 from damage by removing liquid from propane vapor stream 118. Similar to the first embodiment, a feed supply stream 100 enters a distillation column 210 and ethane vapor exits the top of distillation column 210 and flows to heat pump exchanger 220 where the vapor is condensed and then fed back into the distillation column 210. High purity liquid propane then exits the bottom of the distillation column 210 in bottoms stream 112 and splits with a portion exiting the system and a portion flowing to the heat pump exchanger 220. The propane vapors are boiled off and exit the exchanger 220 in stream 118. The propane vapor stream 118 then enters the compressor suction scrubber 420, which removes any remaining liquid entrained in the vapor via recovered liquids stream 134. The dry vapor stream exits the compressor suction scrubber 420 in stream 119 and enters the compressor 270. The remainder of the system 10 of the present embodiment is substantially the same as that of the first embodiment.

Though shown and described individually for simplicity, the various additional components of the second through eighth embodiments (e.g., the reflux accumulator 310, product interchanger 330, economizer 350, HP economizer 370, LP economizer 390, feed interchanger 410, and compression suction scrubber 420) may be combined. For example, in an alternative embodiment shown in FIG. 9, all additional components described in the fourth through eighth embodiments may be combined into one system 10 with the third embodiment. In other alternative embodiments, the additional components described in the fourth and sixth through eighth embodiments may be combined into one system 10 with the second embodiment, or any subset of components may be combined in one system 10.

Referring now to FIG. 9, a ninth embodiment of the present disclosure is illustrated; like parts are designated with like reference numerals. As previously described, the present embodiment is a combination of the components of the third and sixth through eighth embodiments. Similar to the seventh embodiment, feed supply stream 100 enters a feed interchanger 410 prior to entering the distillation column 210. The feed supply stream 100 exchanges heat with the bottoms stream 112, resulting in regulated stream 102 entering the distillation column 210 and interchanged stream 133 entering the HP economizer 370. Similar to the sixth embodiment, the HP economizer 370 separates liquid and vapor with the vapor in stream 129 flowing to the compressor 270 and the liquid splitting between bottoms product stream 114 entering the product interchanger 330 and stream 128 being flashed through the LP economizer control valve 380 to stream 130 and entering the LP economizer 390. The LP economizer 390 separates liquid and vapor with the vapor in stream 132 flowing to the compressor 270 and the liquid stream 131 being flashed through the cooling control valve 260 to stream 116 flowing to the heat pump exchanger 220.

Propane vapor in stream 118 exits the heat pump exchanger 220 and, similar to the eighth embodiment, enters a compression suction scrubber 420. Recovered liquids exit the scrubber 420 in stream 134 and the propane vapor exits the scrubber 420 in stream 119 and enters the compressor 270. The compressor 270 compresses the vapor streams 119, 129, 132. The remainder of the system 10 of the present embodiment is substantially the same as that of the first embodiment.

Referring still to FIG. 9, similar to the third embodiment, ethane vapor exits the top of the distillation column 210 in stream 104 and flows to heat pump exchanger 220. The liquid ethane stream 106 exits the heat pump exchanger 220 and enters the reflux accumulator 310. Stream 109 exits the accumulator 310 and enters the reflux pump 320, which splits the stream with a portion of the stream (overhead product stream 108) entering the product interchanger 330 and a portion of the stream (reflux stream 110) being returned to the distillation column 210.

Referring still to FIG. 9, similar to the fourth embodiment, the overhead product stream 108 and the bottoms product stream 114 enter the product interchanger 330. Similar to the fourth embodiment, overhead product stream 108 exits the product interchanger as stream 125 and bottoms product stream 114 exits the product interchanger 330 as stream 126.

The ability to run the hot discharge of the compressor straight into the distillation column is beneficial to the deethanization process. Using the heat by-product from the compressor is more energy efficient because the heat generated by the compressor is used to drive the deethanization process instead of being dissipated to the atmosphere. Further, smaller pieces of equipment may be used and the distillation column may be operated at a lower pressure and temperature than conventional distillation columns, which rely on the use of a reboiler.

Additionally, the use of the purified propane as refrigerant eliminates the need for a separate closed loop refrigeration unit. This system requires less equipment and is more energy efficient because the heat of compression is used to heat the distillation column. 

What is claimed is:
 1. A system having a low operating pressure for separating ethane and propane from a feed stream, the system comprising: a distillation column having an upper end and a lower end and configured to receive the feed stream and release ethane from the upper end and propane from the lower end; a heat pump exchanger configured to condense the ethane and vaporize the propane released from the distillation column; a reflux control device configured to distribute ethane back to the distillation column from the heat pump exchanger; a cooling control device configured to control an amount of propane entering the heat pump exchanger; and a compressor assembly configured to compress propane vapor exiting the heat pump exchanger; wherein the flowpath from the compressor assembly to the distillation column is configured to flow the compressed propane vapor exiting the compressor assembly into the distillation column to supply heat.
 2. The system of claim 1 further comprising: a feed stream control device configured to control the feed stream entering the distillation column; an overhead product control device configured to control the ethane exiting the system; a bottoms product control device configured to control the propane exiting the system; and a control system configured to actuate the control devices;
 3. The system of claim 1 further comprising a heat rejection device configured to remove heat from the compressed propane vapor.
 4. The system of claim 1, wherein a dehydrating agent removes moisture from the feed stream prior to entering the distillation column.
 5. The system of claim 4, wherein the dehydrating agent is a molecular sieve.
 6. The system of claim 4, wherein the dehydrating agent is a dry glycol.
 7. The system of claim 1, wherein the cooling control device is further configured to introduce vapor to the propane.
 8. The system of claim 1, wherein the control system comprises sensors configured to measure system parameters.
 9. The system of claim 8, wherein the system parameters include at least one of pressure, temperature, composition, or flow rate.
 10. The system of claim 1, wherein the distillation column comprises less than 40 trays.
 11. The system of claim 1, wherein the distillation column comprises less than 35 trays.
 12. The system of claim 1 further comprising a product interchanger configured to exchange the ethane product and propane product.
 13. The system of claim 1 further comprising a reflux pump and accumulator configured to collect and deliver a reflux stream to the distillation column.
 14. The system of claim 1 further comprising one or more economizers configured to remove liquid from the propane vapor.
 15. The system of claim 1 further comprising a feed interchanger configured to regulate a temperature of the feed stream entering the distillation column.
 16. The system of claim 1 further comprising a compression suction scrubber configured to remove liquid from the propane vapor.
 17. A process for separating ethane and propane from a feed stream at low pressure, the process comprising: introducing a feed stream to a distillation column to obtain ethane vapor and liquid propane; condensing the ethane vapor to obtain liquid ethane; removing a portion of the liquid ethane through an overhead product control device; refluxing a portion of the liquid ethane back to the distillation column; removing a portion of the liquid propane through a bottoms product control device; flashing a portion of the liquid propane through a cooling control device to introduce vapor to the liquid propane; vaporizing the liquid propane to obtain a propane vapor having a temperature and pressure; compressing the propane vapor to obtain a propane vapor having a higher temperature and pressure; and flowing the higher temperature and pressure propane vapor to the distillation column to supply heat to the distillation column.
 18. The process of claim 17 further comprising removing heat from the higher temperature and pressure propane vapor through a heat rejection system or bypassing the heat rejection system before entering the distillation column.
 19. The process of claim 17, wherein a dehydrating agent removes moisture from the feed stream prior to entering the distillation column.
 20. The process of claim 17 further comprising a product interchanger configured to exchange the ethane product and propane product.
 21. The process of claim 17 further comprising a reflux pump and accumulator configured to collect and deliver a reflux stream to the distillation column.
 22. The process of claim 17 further comprising one or more economizers configured to remove liquid from the propane vapor.
 23. The process of claim 17 further comprising a feed interchanger configured to regulate a temperature of the feed stream entering the distillation column.
 24. The process of claim 17 further comprising a compression suction scrubber configured to remove liquid from the propane vapor. 